If you are stuck at Receive 30 Souvenirs task, here is simple way to do Chaining Souvenirs:
1. Switch to a Great Buddy or lower. Don't open its gift if it brings one.
2. Avoid Ultra and Best Buddies for about 3 days (long enough that you can expect the souvenir cooldown to be finished). You can still swap between other lower buddies, but don't open their gifts unless you are confident there will be enough time for them to bring another item gift.
3. Open a gift from a Great Buddy. This can only be an item gift, thus putting item gifts on cooldown.
4. Switch to an Ultra/Best Buddy. It should bring a new gift within a minute (and if it doesn't, try restarting the app). Since items are on cooldown but souvenirs aren't (because you waited long enough in step 2), this gift can only be a souvenir. Don't open it.
5. Chain that gift. Swap through other Ultra/Best buddies. For each one, wait until it brings a gift (again, should always be within a minute). Don't open it, swap to the next buddy. Chain until you have enough.
6. Swap back through to get your souvenirs
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