4th pin on lightning cable blackened, both sides.

This is because the charging contacts of the Lightning head are only the leftmost and the rightmost pins (one on each side, four total for both sides), all other contacts in the middle are for data transfer.

If your cable is damaged, I'd recommend buying a new one, as it is almost impossible to fix a broken cable without damaging the casing. If you don't want to pay Apple the full price for their cables, buy one with MFi certification from third-party manufacturers to ensure your cable is legitimate, and is officially able to work with your device.

Although, it would have been wise to take it back immediately after purchase, but I don't know when that was or if you are still in that one year warranty period of if you have Apple Care.

If you don't like to buy a new cable, you can instead get a Fiberglass Scratch Brush, and try to gently rub off the corrosion on the connector. However once corrosion has started to form on a metal, it will always reappear, but you might find other uses for a brush like that and it wouldn't hurt to get one anyways.

Amazon's own Amazon Basics braided Lightning cables are of good quality.

Also, braided Lighting cables from Anker and Belkin are also of great quality.

All of these have a great replacement policy if the cable fails in any respect.

Both Amazon and Anker just recenly replace my braided Lightning cable and a heavyweight Lightning to USB-C cable that decided to just stop working suddenly after about a year.

Both Amazon and Anker have terrific customer service.

My experiences with Belkin electronics device customer service have been both so-so and pretty good, depending on the product and issue and on a particular occasion, they gave me a updated replacement product that had been out of warranty for almost a year, but they did it because they had assured me that the product I purchased ( a very expensive 3 antenna MODEM/router were very reliable and it should have lasted much longer than it did.

So, they offerd me an free, new replacement upgraded MODEM/router of similar design and cost.

BUT, one other time, they wouldn't replace a very expensive computer digital audio cable that failed just outside of Belkin’s own warranty period.

I had an extended warranty for this fairly expensive audio cable/adapter setup from the music/computer/audio place I purchased this cable from, so I got another free cable and specialised adapter from them, at no cost.

But I had to go get it from the retail store I originally purchased from, instead of just waiting for it to be shipped to my address from Belkin.

So, Belkin seems to have different warranty policies for all of their myriad of computer/audio/electronics products.

Anyhoo, Amazon Basics braided Lightning cables, and ones from Anker electronics and other third party makers of better quality braided and heavyweight computer cables can be found fairly cheaply, inexpensively.

Lightning cables ate just as common as any type of USB cable. and are no longer very expensive to purchase.

Sorry to learn you are still not back to work because of the Pandemic.

Best of Luck to You!

Be Well...Stay Well!

In case you can purchase later, when finances pick up.

https://www.amazon.com/s?k=Amazon+Basics+braided+Lightning+cable&ref=nb_sb_noss_2

https://www.amazon.com/s?k=Anker+Lightning+cable&ref=nb_sb_noss_2

https://www.amazon.com/s?k=Belkin+Lightning+cable&ref=nb_sb_noss_2

Again, Best of Luck to You!

Just purchase a new cable and stop playing around with the damaged one.

You can find good quality Lightning cables cheap online, like from Amazon.

Just purchase a new Lightning cable already.