In Pokemon Masters your sync pairs have multiple levels associated with them. There is their base level and level cap, but there’s also the stars that they have as well. Sync Pairs can go all the way up to five-stars, but if you want to increase stars for a sync pair from three to four you’re going to need a specific item to do this.
To increase stars in Pokemon Masters for a sync pair you will need to increase potential. This can only be done in the Pokemon Center by speaking with Trinnia (green NPC) and selecting the Increase Potential option in the team menu. Depending on the level of stars the Sync Pair currently is, you will need different items to increase stars.
To level a 3-star to a 4-star you will need a 3-Star Power-Up Ticket, which is the only item that can increase a sync pair’s number of stars. If you want to level a 4-star to a 5-star you will need a 4-Star Power-up Ticket. Regardless, to increase stars you will need to apply 20 tickets of the right level to the character you want to raise stars.
Promotion tickets that Increase Stars for Sync Pairs come in different varieties. There are bronze tickets, silver tickets, and gold tickets. Bronze will be used to transition from 3-star to 4-star. Silver are used to transition from 4-star to 5-star. Gold tickets will be used to transition from 5-star to max level.
You don’t necessarily have to apply 20 tickets all at once. You can apply one ticket at a time and you will still increase the stats of your character. Each ticket type has a different stat boost associated with it which raises the HP and all other Stats of your Sync Pair.