I understand that case is not solved by change APN like you write and I quote ?
Then it's like your ISP not pass you internet and block you by some purpose.
Do step after step
1) Try use webpage with proper DNS from ISP
You have a good DNS, MikroTik have got only DNS from ISP and end user have got MikroTik itself or ISP.
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But you must remove that 192.168.88.1 from DHCP Server and pass only ISP DNS IP because your Chateau not have a ALLOW to use 192.168.88.1, I see that here: #17
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You must add this option or remove 192.168.88.1 from DHCP Server Network tab. One of two you must do.
This step maybe have necessery fix a TTL value what is here
https://wiki.mikrotik.com/wiki/Manual:I ... throttling means:
/ip firewall mangle add action=change-ttl chain=postrouting new-ttl=set:65 out-interface=lte1 passthrough=yes
Then try any webpage.
With that ATT in USA show at any webpage message "It looks like you want to use data but have none available. You may need to add data." and then we know what to do.
2) Try disable "Use Network APN".
This APN must be used inside lte1 interface if you have few of them.
APN: you should use your of course, my "internet" is common/default one
IP Type: change from auto to IPv4
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Remember that you must select proper APN Profile in lte1 General tab.
Why? Because you show us at screenshot that you use TWO APN Profiles. Maybe you create it but it is not selected inside lte1 ?
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3) Spoof lte module vendor that you have other LTE device.
You say it's work out-of-box in LHGR who use R11e-LTE6, that card IMEI almost work at every plan :).
If you get to that point then best way will be get IMEI of that LHGR unit and not use that device. Use IMEI from LHGR inside Chateau LTE12.
I edit this answer/post if ad 1&2 not help and write you a way here.
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