Two critical suppliers (the payment provider and the cloud host, without which the checkout stops), two important ones (the carrier and the newsletter tool)
The text tiers four suppliers, but the register in Table 19.4 has no carrier row, so one important supplier is unmanaged. Also, §19.2 says the payment processor needs PCI DSS plus an ISAE 3402 or SOC 2 report, yet the register lists only PCI DSS under Assurance. The register should match the text.