Older versions of iPhone OS aren't new enough to have modern certificate authorities trusted, meaning only sites using older certificate authorities are able to have a secure connection.

Here are links to modern Certificate Authorities that may not be trusted on older devices (some other complications may prevent sites using these certificates from working, those can not be fixed by these.)

Pirate Ship Canada Post Free 〈PREMIUM | 2027〉

Word on the docks was about a scrappy crew called Pirate Ship — shipping software that promised “no monthly fees, no markups,” and access to steep USPS and UPS discounts for free. Mira created an account (no credit card, no fuss) and began to rate-shop: USPS services, UPS Ground and even Pirate Ship’s Simple Export Rate — all passed through at carrier-negotiated discounts. Labels printed quickly, tracking numbers appeared like tiny compass bearings, and $100 of insurance came attached to many UPS labels at no extra cost. The interface was breezy enough that Mira could batch-print dozens of labels between stirring her morning tea and feeding the cat.