Each expense carries a split — half each, or whatever proportion your arrangement uses. The app works out who owes what.
Requesting reimbursement records the request and its date. Marking it paid records that too, so "I paid you back for that" stops being a matter of memory.
Money doesn't move through us
CalmHandoff records what's owed and what's been paid. It doesn't move money. Pay each other however you already do — bank transfer, whatever your order specifies — then mark it paid here.