The OP tipper in that thread was probably an Uphold user while you’re a Gemini user. That’s why they couldn’t tip you and got that message.
Someone else replied in the thread saying:
Please be aware anyone whose Creator account is connected to the partner exchange you are not connected to will appear as a verified creator who is not configured to accept tips from you. So if your browser is on Gemini and a Creator is on Uphold you cannot tip them. Cross-exchange tipping is not possible right now, and would require significant changes to Rewards (like migrating to an L2 chain) to make it possible due to gas fees.
For the record, I accessed your Reddit profile and I see that you’re properly verified and tippable, but I am using Gemini so that probably explains it.