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Sectigo provide a guide on the creation of .csr files here: https://support.sectigo.com/Com_KnowledgeDetailPage?Id=kA01N000000zFIo.
Q: Why is My order stuck in Applied?
Applied generally means that the request has been sent for manual review. Checking the following may help:
1. CAA records of all FQDNs & domains contained in the certificate request
2. Umlauts, diacritics etc in the org name or province/state etc - at some time that caused a manual review of the first request which included these characters by Sectigo
3. org names that are exactly 64 *bytes* and beware that single UTF-8 characters might count as 2 bytes
4. block-listed words in the requested domains like "test", "demo" etc
5. some very special encoding of ECC keys caused stalled applied cert requests
6. reasons given by the Sectigo Order Checker https://secure.trust-provider.com/products/ORDERSTATUSCHECKER
If a certificate has been in applied for more than a few hours, please contact support: https://sectigo.com/support-ticket/