welcome_message
Note that this is a Fedimint-defined field and does not require the fedi:
prefix. Read the Fedimint documentation page before using this field.
This message will be displayed to users immediately after scanning the federation invite code, so it should include any information that is relevant to the user before they join on what to expect from the federation.
Structure
Unicode string HTML formatting is NOT supported
"welcome_message": "Welcome! Please read the terms of service on the next \
screen before joining the federation."