Camera says there's no SD card

First, I would try a second card - buy one if necessary. I have so many (and an automotive grade Gathers (SanDIsk OEMd best I can tell) 8GB from a Japanese J1 a6300, tweaked with OpenMemories: Tweak the seller shipped with it and fixed before selling it), where if I know my automotive grade card doesn't work, the slot is probably bad as automotive cards have much higher TBW ratings and more insertion/removals. If the issue remains, check the slot with a flashlight. If any of the pins look bent or out of place (if you need to get a visual reference, see if you can ask a friend or family member who owns a camera to show you what a good slot looks like). Brand doesn't matter, it's all the same part.

There is a second possibility: A lot of legacy cameras do not support SDXC cards, which are increasingly becoming the "norm" with 64GB and beyond :-(. Some of these old cameras do not like these cards, or only low-capacity XC cards like 64GB and NOTHING MORE. Try an SDHC card (8-32GB) and see if the camera accepts it, especially if the card causing issues is SDXC.

If the pins are bent, it will either require a new mainboard (and sensor calibration) or a complete camera replacement. That being said, you can probably buy the part online, open it up yourself, and solder a new one on - but the only way that usually works out as being worth it is on cameras that are relatively expensive, such as the Sony Alpha and other mirrorless bodies. Cheaper P&S and legacy bridge cameras tend to be a tougher proposition when you do the economic math.