Just for information/comment, I used the app to post my TM30 this morning, having arrived back in Thailand yesterday, and left the field asking for the TM6 number blank, filling in date and arrival port.
The app took my data, no problem and searching, in the app, I found my posting, so I assume all is OK.
I haven't searched on the intranet, is this necessary or recommended?
TLDR : Answer Summary
After submitting a TM30 form through the app, it is confirmed that users can find their registration on the app itself. Taking a screen grab serves as a receipt, and users should print it for their records. The TM6 number is not a mandatory field when submitting the TM30. However, for first-time users or for those unfamiliar, it's recommended to check back in the app to ensure the submission was processed.