Add signers

Attach one or more signers to a draft envelope. Each signer has a role (signer, approver, viewer) and an optional order field for sequential signing.

POST /v1/envelopes/{id}/signers

curl https://api.permissio.us/v1/envelopes/$ENV_ID/signers \
-H "Authorization: Bearer $PERMISSIO_KEY" \
-H "Content-Type: application/json" \
-d '{
  "name": "Avery Lin",
  "email": "avery@example.com",
  "role": "signer",
  "order": 1
}'

When two signers share the same order, they sign in parallel. When orders differ, Permissio waits for the lower number to complete before notifying the next.