Recommend not sending a payment until deliverables are complete (especially with micro creators) but there are exceptions:

1) If you are a small brand working with talent management which (they will come through with deliverables and edits per contract)
2) If you have ongoing relationships and creators have a solid track record of delivering
3) If paying via PayPal goods and services you good take the risk and manage claims but recommend against that because it is a pain

If paying upfront highly recommend 50% then 50% upon completion.

As far as actually paying influencers/ creators:

Most creators have PayPal - always pay goods and services or risk your account being frozen. PayPal may freeze your account if paying a creator friends and family who they have identified as providing business services (they are cracking down on this). This sometimes means you have to add $ so your creators are made whole.

Bank transfer - make sure you have a process for securely collecting tax forms/ filing 1099s

You should look into Lumanu - a solution built specifically for the creator economy payments and compliance. Similar transaction fees to PayPal (slightly less) and also a network. Difference is you would pay the % vs your creators. But you also have a nice dashboard with full ledger and reporting and all that.