What each check needs

Checks	Required
`X402-01`–`05`	nothing
`X402-06`, `07`	`STELLAR_PRIVATE_KEY`
`MPP-01`	`MPP_PAYER_SECRET`, `MPP_STELLAR_NETWORK`
`MPP-10`–`12`, `14`	`COMMITMENT_SECRET_HEX`, `MPP_STELLAR_NETWORK`
`MPP-13`	the above, plus `CHANNEL_CONTRACT_DISPOSABLE` and an explicit opt-in
`MPP-10` parameters	`--expect-token`, `--expect-from`, `--expect-to`, `--expect-refund-period`

The fixture servers need their own values — see .env.example. Those are only required to run the bundled fixtures, not to test a third-party service.