How to file income earned in first state but paid during the time in second state?

I was a resident of MA working for one employer, but I quit and moved out of MA to MT during the second half of 2025.

(1) I received payment for expat expenses related to work I did abroad in 2024. This was paid out and taxed in December 2025 as part of my 2025 tax return.

(2) There was also one payment made after I left both the employer and MA, due to a prior miscalculation.

(3) I also worked physically in MA during December 2025, but by then I was already a resident of MT.

I am filing both state tax returns as a part-year resident for both MA and MT. For clarification, are all these MA-sourced incomes, even the expat expense for work abroad? Should I file them as "MA income while nonresident" on my MA tax return and as "MT portion" on my MT tax return for all three payments?

Afterwards, will MA and MT tax returns be considered for tax credits from either state? Would MA give tax credits for MT-reported income for any taxes paid to MT? Should MT give tax credits for MA-sourced income for these three pays? I am not sure why on my tax returns that MT gave tax credits but MA also gave credit for all the taxes accrued for MT, as I only paid MA taxes.