You wrote " I traced it with a light pen", I have never seen that this is working on single mode fiber. I thought it only works for multimode.
And if your fiber is multimode, and the SFP:s are LX (single mode) that will be a problem. It can maybe work for a very short range with 10G, it reaches a bit longer with 1G, so the advice from @balaji to test with 1G is good. Or try with SX.