Data miners:
"Link Charges can be used to enter Mega Raids in place of Raid passes. Link Charges are required to enter Mega Raids Remotely.
Earn Link Charges from activities such as Weekly Challenges, Campfire Check-Ins, and opening Gifts."
While I think there are WAY too many different currencies in this game, it sounds like these will be obtainable from ordinary game mechanics.
by MarkusEF