Dropping the local db and restarting with the replica set option worked for me.
Next issue: I’m running version 6.0.3 and tried to add a Raspberry Pi in the mix. However, the last version that works is 4.4. rs.status() complains that:
remote host has incompatible wire version: Server min and max wire version (9,9) is incompatible with client min wire version (17,17).You (client) are attempting to connect to a node (server) with a binary version with which you (client) no longer accept connections. Please upgrade the server’s binary version.
Can I downgrade my 6.0.3 version to be 4.4, or is that not advisable? If not, how would you suggest I add a replica set member with 4.4?