Register bank mismatch

A shop compares its own register log against the bank statement, day by day. Both inputs are rows "date,amount" (date like "2026-03-01"; amount an integer, negative for refunds; a date can have many rows in either input). The two agree on a date when the SUMS of that date's amounts match; a date absent from one side counts as sum 0 there. Return the dates that disagree, sorted ascending. Example: register ["2026-03-01,50", "2026-03-01,25", "2026-03-02,40"] vs bank ["2026-03-01,75", "2026-03-02,35"] gives ["2026-03-02"].