iMessage stopped working after I installed my eSIM

Make sure that your primary (old) SIM card is still set as the default voice line and that the (new) eSIM card is used for mobile data. Here is the installation guide with the exact description of all priority settings. Make sure that iMessage is enabled and that your phone number and email address are listed correctly. Sometimes, a simple restart can also solve problems with iMessage. Turn off your device, wait a few seconds, and then turn it back on.