[Solved] Tuya T2-U module only allowing 4 data points—how to enable more DPs for custom functions?

I'm trying to add custom functions to a Tuya T2-U development module (later to be hooked up to an Arduino with sensors) so that I have 5 or 6 data points available for various smart automations. I'm using official Tuya everything - module, Cloud module burning app, Module debugging assistant, etc. I've got 4 DPs working perfectly, but no matter how I tweak the other functions in Tuya's developer platform using different DP numbers, data types, etc, they are failing to report changes to the online logging feature or my Tuya Smart phone app. Spent weeks on this - I'm going to scream.

I've got the development 'device' configured as a simple switch (which should allow dozens of DPs) but even when I choose the default switch (boolean) DPs, or other standard DPs, they all fail. No errors reported, just nothing. Seems I'm only allowed three 'value' DPs, and one boolean. Have refreshed and re-burned many times. Tuya support engineers have responded, but with no solution yet.

Someone save my sanity please!

PS: I'm using the good old MCU SDK (not TuyaLink or TuyaOS), and Tuya's own T2-U firmware option.

Although not officially well documented, some device types have DP limitations (e.g. 4-5 active at the same time). Check:
In Tuya IoT Platform - Product - Function Definition whether all DPs have a status of "Published".
Remove default DPs and leave only your own - sometimes too many defaults block others.

Let us know how you managed to fix it.

>>21592304 Thanks for the ideas. Unfortunately that 'Published' status information must have been deleted in the developer platform. There's nothing like it, either in the main 'Function Definition' interface, or the ' Add' dialogues for standard and custom functions. I have definitely tried stripping down all functions to those I really need, with no standard ones used at all, and nothing superfluous. It doesn't help. I've got the four good ones working, but I need five! Six would be ideal. I'm thinking the same as you about some kind of unwritten limitation to the number of DPs in certain products, but Tuya's support people have been acting like there's no such issue.

I would create a new product from scratch, perhaps an environmental sensor or something, which would presumably allow more DPs than a switch, but when I try this I am only offered TuyaLink or TuyaOS as options. I want the MCU SDK that I'm familiar with, but they seem to be steering people away from it now. So I'm marooned on this legacy product trying to add just one more DP!

I've sorted out the problem. After making any changes online, besides burning the adjusted firmware I needed to:
1. Reset the module using the Basic Functions / Reset button in the debugging assistant (not sure how significant this step is vs the onboard button), and...
2. Completely remove the device from the phone app and go through the re-pairing step again.
I'd been resetting via the physical button, and only removing the app from the home screen. It was still active in the background. I was scared of completely removing it in case I was unable to pair my device again (I was stuck for days, trying onboard button press variations, until the debugging assistant did the trick). I was also scared of losing the four good DPs that I had in hand, which would have allowed partial functionality at least.
So, on to the next stage.

After making changes to functions on Tuya's web interface:
1. Download the new json file and burn the adjusted firmware onto the module using Tuya's Cloud Module Burning Authorization Platform.
2. Load the new json file into Tuya's debugging assistant which is available under the Hardware tab in the Developer Platform, near the json link. Ignore any update errors when the assistant app opens, by the way. It worked fine for me updates or not.
3. Reset the module using the Basic Functions / Reset button in the debugging assistant (not sure how significant this step is vs. the onboard button).
4. Completely remove the device from the phone app and go through the re-pairing step again, which should be offered automatically if the module is attached and live in the debugging assistant.
5. Send some test values to your DPs with the debugging assistant.
6. Check the online logs (Product / Device / Device Details, and change server to whatever shows results).
7. Hopefully you'll see your latest test values reflected in the logs. Celebrate!