Noro pattern confusion

I am working on a noro pattern called Shinju which is a women’s sleeveless top.

Just starting on the back and it calls for a pattern that says yf, sl 1, k1, psso, and repeat but it creates a decreased stitch yet it’s not supposed to decrease yet. What am I doing wrong ?

Welcome to KH. There is a comment on Ravelry about an error, is this where you are? The comment is from 10 months ago. What is the next line in the pattern? Are stitch counts given? I think that would help someone to help you.
Need help with this pattern. Error on row 11 on the row 1-12 repeat on the back I have contacted customer service, and have had no response
https://www.ravelry.com/patterns/library/shinju-2/comments
I see no mention of errata.

Welcome!
The stitch combination should be defined at the beginning of the pattern or possibly at the end of the pattern.
If the preceding stitch is a knit stitch, bring the yarn forward between the needles, slip one, then bring the yarn over the right hand needle to the back and knit one. Finally pass the slipped stitch over. Probably the slip stitch goes over just the k1 but you can try it on a swatch to make sure it gives you the pattern stitch you can see.

The yarn over increase will balance out the slip stitch decrease.