Get back to basics, firstly the agent service account on the primary doesn't need any access to the copy location on the secondary server. It doesn't know about it and indeed, should not have access. The agent service account on the secondary must be able to access the share on the primary unchallenged.

On the primary you have created a folder to hold the LS backups, this folder is shared, list the share permissions below

Now list the security permissions applied to the folder

Now list the agent accounts for the primary node and secondary node sql server agent services