No idea what is different in Nazjatar, but mapinf is nil and the routine exits with false. Maybe a bug in the blizzard api.

Replace

with

I really hope Guppet gets updated. In the meantime, a simple workaround in Nazjatar is just using the ground mount or fly mount only binds rather than the smart mount. Yes, it can be a slight inconvenience but it's not so bad in the overall scheme as half the reason I love this addon is the pet feature.  Sorry, I'm totally LUA clueless and the fixes below were all greek to me. 

For the addon to work in Nazjatar, I edited the "GupP_Mount_CanFlyThisContinent()" function in the GupP_mount.lua file:

local function GupP_Mount_CanFlyThisContinent()

                -- To avoid errors

                if InCombatLockdown() then return false end

                local continent

                if C_Map.GetBestMapForUnit("player") == 1355 then

                                continent = "Nazjatar"

                else

                                continent = MapUtil.GetMapParentInfo(C_Map.GetBestMapForUnit("player"), Enum.UIMapType.Continent).mapID

                end

                if continent == 875 or continent == 876 or continent == "Nazjatar" then -- BfA, and also Nazjatar

                                 if not IsSpellKnown(278833) then -- BfA Pathfinder

                                                return false

                                end

                elseif continent == 619 then -- Broken Isles

                                if not IsSpellKnown(233368) then             -- Broken Isles Pathfinder

                                                return false

                                end

                elseif continent == 572 then -- Draenor

                                if not IsSpellKnown(191645) then             -- Draenor Pathfinder

                                                return false

                                end

                elseif continent == 12 -- Kalimdor

                                or continent == 13 -- Eastern Kingdom

                                or continent == 101 -- Outland

                                or continent == 424 -- Pandaria

                                or continent == 113 -- Northrend

                                or continent == 948 then -- Maelstrom (Deepholm)

                                if not select(13,GetAchievementInfo(890)) then -- Expert Riding

                                                return false

                                end

                else

                                return true

                end

end

I don't have flying yet but if anyone who does and tests this and it doesn't work, please let me know. :)

In reply to fishermansfriendmenthol:

Hi - I swapped out the function you mentioned with your code and got a couple of errors. Thanks for trying to fix this. I hope this is useful in finding a fix.

Firstly, on entering the game:

Date: 2019-07-12 00:09:36
ID: 1
Error occured in: Global
Count: 1
Message: ..\AddOns\GupPet\GupP_Mount.lua line 1:
'=' expected near 'function'
Debug:

Locals:

AddOns:
Swatter, v8.2.6241 (SwimmingSeadragon)
Ace3, v
AdvancedInterfaceOptions, v1.3.0
AllTheThings, v1.9.5b
AngryWorldQuests, v
AskMrRobot, v78
AucAdvanced, v8.2.6295 (SwimmingSeadragon)
AucStatSimple, v8.2.6232 (SwimmingSeadragon)
AucUtilFixAH, v8.2.6235 (SwimmingSeadragon)
BagBrother, v
Bagnon, v8.2.0
BattlePetBreedID, vr199
DBMArchaeology, v
DBMCore, v8.2.3
DBMDefaultSkin, v
DBMStatusBarTimers, v
Excavatinator, v3.0
FishingAce, v0.8.9
GatherMate2, v1.44.2
GryphonsRemover, vv8.2
GuildMemberOnline, v1.8
GupPet, v8.0.1.05
LibSharedMedia30, v3.0-110
SlideBar, v8.2.6273 (SwimmingSeadragon)
Stubby, v8.2.6274 (SwimmingSeadragon)
BlizRuntimeLib_enUS v8.2.0.80200 <none>
(ck=2d0)

and

Date: 2019-07-12 00:13:14
ID: 1
Error occured in: Global
Count: 1
Message: ..\AddOns\GupPet\GupP_Mount.lua line 1:
'=' expected near 'function'
Debug:

Locals:

AddOns:
Swatter, v8.2.6241 (SwimmingSeadragon)
Ace3, v
AdvancedInterfaceOptions, v1.3.0
AllTheThings, v1.9.5b
AngryWorldQuests, v
AskMrRobot, v78
AucAdvanced, v8.2.6295 (SwimmingSeadragon)
AucStatSimple, v8.2.6232 (SwimmingSeadragon)
AucUtilFixAH, v8.2.6235 (SwimmingSeadragon)
BagBrother, v
Bagnon, v8.2.0
BattlePetBreedID, vr199
DBMArchaeology, v
DBMCore, v8.2.3
DBMDefaultSkin, v
DBMStatusBarTimers, v
Excavatinator, v3.0
FishingAce, v0.8.9
GatherMate2, v1.44.2
GryphonsRemover, vv8.2
GuildMemberOnline, v1.8
GupPet, v8.0.1.05
LibSharedMedia30, v3.0-110
SlideBar, v8.2.6273 (SwimmingSeadragon)
Stubby, v8.2.6274 (SwimmingSeadragon)
BlizRuntimeLib_enUS v8.2.0.80200 <none>
(ck=2d0)

On trying to auto call a mount

Date: 2019-07-12 00:14:14
ID: 3
Error occured in: Global
Count: 1
Message: [string "GupPet_AutoMounten()"] line 1:
attempt to call global 'GupPet_AutoMounten' (a nil value)
Debug:
[string "GupPet_AutoMounten()"]:1: in main chunk
[C]: RunScript()
..\FrameXML\ChatFrame.lua:2171: ?()
..\FrameXML\ChatFrame.lua:4836:
..\FrameXML\ChatFrame.lua:4783
[C]: ChatEdit_ParseText()
..\FrameXML\ChatFrame.lua:4497:
..\FrameXML\ChatFrame.lua:4496
[C]: ChatEdit_SendText()
..\FrameXML\ChatFrame.lua:2991:
..\FrameXML\ChatFrame.lua:2984
[C]: RunMacroText()
..\FrameXML\SecureTemplates.lua:441: handler()
..\FrameXML\SecureTemplates.lua:632:
..\FrameXML\SecureTemplates.lua:580
Locals:
(*temporary) = nil
(*temporary) = "attempt to call global 'GupPet_AutoMounten' (a nil value)"

AddOns:
Swatter, v8.2.6241 (SwimmingSeadragon)
Ace3, v
AdvancedInterfaceOptions, v1.3.0
AllTheThings, v1.9.5b
AngryWorldQuests, v
AskMrRobot, v78
AucAdvanced, v8.2.6295 (SwimmingSeadragon)
AucStatSimple, v8.2.6232 (SwimmingSeadragon)
AucUtilFixAH, v8.2.6235 (SwimmingSeadragon)
BagBrother, v
Bagnon, v8.2.0
BattlePetBreedID, vr199
DBMArchaeology, v
DBMCore, v8.2.3
DBMDefaultSkin, v
DBMStatusBarTimers, v
Excavatinator, v3.0
FishingAce, v0.8.9
GatherMate2, v1.44.2
GryphonsRemover, vv8.2
GuildMemberOnline, v1.8
GupPet, v8.0.1.05
HandyNotes, vv1.5.5
HandyNotesDungeonLocations, v1.46
HandyNotesSuramarTelemancy, v1
HandyNotesWarfrontRares, v0.5.0
IceHUD, v1.11.11
Immersion, v1.1.0
Informant, v8.2.6246 (SwimmingSeadragon)
LargerMacroIconSelection, vv1.4.2
LibSharedMedia30, v3.0-110
MageNuggets, v6.1.1
MageNuggetsCooldownMonitor, v6.0.2
MageNuggetsStatMonitor, v6.0.2
Mapster, v1.8.3
MinimalArchaeology, v8.2.0
Omen, v3.2.2
oRA3, vv8.2.1
Outfitter, v5.22.1
ParagonReputation, v1.24
Pawn, v2.2.45
PetCaught, v1.1
PetTracker, v8.1.2
PetTrackerConfig, v8.1.2
Postal, vv3.6.0
Prat30, vr1195
Prat30Libraries, v
RareScanner, v5.5.2
Recount, vv8.2.0a
Rematch, v4.9.10
Routes, vv1.6.3
SellTrash, v
Skillet, v4.08
SlideBar, v8.2.6273 (SwimmingSeadragon)
Stubby, v8.2.6274 (SwimmingSeadragon)
TomTom, vv80200-1.0.3
TransmogTokens, v1.4.9
WeakAuras, v2.13.4
WonderRep, v2.1.1
ZPerl, v5.7.7
ZPerlParty, v
ZPerlPartyPet, v
ZPerlPlayer, v
ZPerlPlayerBuffs, v
ZPerlPlayerPet, v
ZPerlRaidFrames, v
ZPerlRaidHelper, v
ZPerlTarget, v
ZPerlTargetTarget, v
BlizRuntimeLib_enUS v8.2.0.80200 <none>
(ck=6b6)

In reply to ianhend:

The only clue I can find points to an error in the first line of the GupP_Mount.lua file. The first line of the file should be "local function GupP_Mount_CanFlyThisContinent()".  

I put up the entire contents of my GupP_Mount.lua on paste bin at https://pastebin.com/MdSu7GaC if you'd like to do a compare. 

Hope that helps!

In reply to fishermansfriendmenthol:

 Thanks. I didn't compare the file, but I did completely replace the file with what you put on Pastebin.

I was in Boralus when I logged in, and no error.

Summoned mount ok in Boralus.

Portaled to Nazjatar - No error

Summoned mount in Nazjatar and it worked.

I guess I must've missed something.

Confirmed that the code on the Pastebin link works. Thanks again for taking a look at my comments.

To fly with "Battle for Azeroth Pathfinder":

replace in GupP_Mount.lua

with

In reply to MachinelfGaming:

 In Nazj, use shift+shortcut, it will force use a ground mount. However, now that flying is being unlocked, there are many other problems. 

In reply to MachinelfGaming:

Unofficial version of GupPet that works in Naz with ground mounts can be downloaded from here:

https://bitbucket.org/grimmlabs/guppet/src/master/

Flying mounts to come when I can actually spot the data.

In reply to grimmtooth:

A quick fix seems to be to look specifically for the Nazjatar zone:

function GupPet_CanFly()
  local zone = C_Map.GetBestMapForUnit("player")
   if (zone == 1355) then
     if not IsSpellKnown(278833) then
      return false
    else
       return true
    end
  end
[...]

LUA isn't a language I'm familiar with, so I'm not sure why I couldn't get it to work in GupP_Mount_CanFlyThisContinent() and had to hack it in to GupPet_CanFly() instead, but hopefully it'll help someone.

Obviously IsSpellKnown(278833) has to be added to GupP_Mount_CanFlyThisContinent() to get flying in the other areas, but most of that code is already in place.

In reply to houseofmabel:

Yep, which is exactly what I did in my "local" mods to the addon.  Oddly, Mechagon doesn't have a problem. Yet another half-finished, half-tested addition to the Blizz API.  Five bucks says they never fix it.

In reply to houseofmabel:

Thanks, I've made changes in this vein and we'll see how they work.  I don't have pathfinding yet but the changes make sense so go grab

https://bitbucket.org/grimmlabs/guppet/src/master/

and give it a whirl if you like.

I'll get caught up eventually :)

In reply to grimmtooth:

 hi, can fix islands expeditions cant use any mount? thanks with any help

In reply to milotic03:

Can you run the  addon with debug mode enabled and give me a list of what zone numbers are reported?  I apologize, I've been too lazy to run any expeditions at all.

To do so, uncomment line 43 in GupP_Mount.lua and reload the game.  The zone ID will be printed every time you attempt to mount (successful or not).

In reply to grimmtooth:

1037, -- Whispering Reef

source allthethings addon

still missing 2 maps id blossom village and crestfall i try search later

In reply to milotic03:

Thanks!  I've added those zones to the no-fly check and uploaded the changes to Bitbucket - https://bitbucket.org/grimmlabs/guppet/downloads/

Debug mode is turned off in the uploaded version, you'll have to turn it back on if you install this.

Happy no-flying!

In reply to MachinelfGaming:

Cool. I've merged these into my "local" version and posted it here:  https://bitbucket.org/grimmlabs/guppet/src/master/

I don't have Pathfinding yet so I can't test that aspect but the changes I made at least don't chuck an error. 

Thanks for the note, I've credited you in the changes I made, hope that's okay.

I've posted to both authors weeks ago and have received no response.  Maybe I have the wrong dudes.  Anyway, I have modified the addon locally so that it will work correctly in warfronts that are not in patrol mode (i.e. the ones where you are restricted to ground mounts).  This isn't their fault, the Blizzard API call returns a false positive for "can I fly here?" in those zones.

If interested, you can find my changes here: https://bitbucket.org/grimmlabs/guppet/src/master/

If you can't access it, please let me know.

At some point I'll actually try an expedition and if I find problems I may make another change.

Meanwhile note there are several fine alternatives out there, as long as you don't care for companion (i.e. battlepet) stuff. GoGoMount and BeStride are both excellent, but there are also many others.