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The first post of this thread is a WikiPost and can be edited by anyone with the appropiate permissions. Your edits will be public.
What are you trying to do? Continue using your main number with iMessage or are you trying to use the local eSIM number for iMessage?

To continue using the main number for iMessage, just leaving your main SIM turned on and activated for iMessage should work.
Thanks. I think I’ve sorted it out. Just want to keep using iMessage like normal. There’s no phone number associated with the local SIM, it’s data only. Keeping my primary sim/number active while switching data to the local SIM, and turning off send as text, seems to have done the trick.
 
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