I posted a photo for the first time and it was rejected with the error: quality problem.

Don't be too disappointed if your sunset gets rejected.  Adobe Stock already contains 26.5 million sunsets; and 36.5 million sunrises. 😯  There's too much competing inventory in this keyword.

For better results, look for subjects that have way less representation -- i.e. shipping cartons, soda cans, plastic bottles.

Also read your Stock Contributor User Guide for more tips.

• https://helpx.adobe.com/stock/contributor/help/reasons-for-content-rejection.html
• https://helpx.adobe.com/stock/contributor/help/quality-and-technical-issues.html
• https://helpx.adobe.com/stock/contributor/user-guide.html/stock/contributor/help/photography-illustrations.ug.html
• https://helpx.adobe.com/stock/how-to/tips-stock-image-acceptance.html
• Model/Property Releases:
  https://helpx.adobe.com/stock/contributor/help/model-release.html
  https://helpx.adobe.com/stock/contributor/help/property-release.html

In addition to the lens spots pointed out by @Abambo you have a significant amount of clipping in the image. This pure black area has no detail whatsoever.

It's a nice picture. You should stamp out the undefined "stains" in your picture and may be also eliminate the power line at the bottem of the image and try again.