Merge your SPF records into one
A domain must have exactly one SPF record. If a new service told you to add another, or you need to add a service to the one you have, this builds the single record to publish.
Why it matters
Two SPF records is the same as none.
SPF is the record that lists which services may send email as your domain. When a receiving server finds two of them, it doesn't pick one: it treats the whole check as failed. Your mail then looks forged, and goes to spam or bounces.
It happens easily. A newsletter tool, a booking system or a website plugin says "add this SPF record", and a second one appears beside the first. The fix is to take every entry from both and put them in one record, which is what this does.
It also checks the record against the limit of ten lookups, keeps the strictest ending the records agreed on, and tells you what each entry allows.
More on SPF, DKIM and DMARC in the guide to email that isn't arriving.