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Hi robert

Looking on both your images I conclude you did absolutely no postprocessing at all. Additionally there seem to be some exposure issues in both images. The second is over expose, the first seem to be underexposed. Lets look at the reason sited for rejection:

Artifacts

Artifacts includes noise, gains, color fringing, and other artificial coloration that is many times present in the body of the image. Grains are dark spot that are usually more visible in the dark and shady areas of the image, and is more visible at smooth areas magnified at 100 to 200%. Grains are also visible in smooth areas. As you view these areas you'll notice if there's a light spectrum of colors that should not be there. For example shadow having colors of purple, blue, pink etc. and not solid black. Color fringes are usually at the edges, most of the times purple. To correct these you need to, with an editing software, apply small amount of postprocessing. Be careful not to make it obvious.

Knowing your camera is also important. You need to read the manual about your camera so that you can use correctly the different features base on the environmental condition or subject. For example low light might require a little exposure compensation, or to ensure reduced grains/noise you might need to ensure your ISO is set low, and so on. It is best to avoid the use of flash.

The second image rejected for technical error: As was highlighted by ricky, there is the presence of the flare. That is a technical problem. Your composition is also another. Your image is taken too close. The third I see is what is highlighted by ricky and abambo, contrast is missing, also it is overexposed. The image itself is lacking vibrancy and is pale in appearance. It is better to include a little of the surrounding along with your subject so that customers are able to crop, or add captions.

Here are some links you can benefit from:

tagproducts_SG_STOCK-CONTRIBUTOR_i18nKeyHelppagetitle  Read up on all the links especially the "Stock Contributor User Guide"

tagproducts_SG_STOCK-CONTRIBUTOR_i18nKeyHelppagetitle Click/tap on each of the links to the left menu; read up on all the relevant topics, and reference links.

Reasons content is rejected at Adobe Stock

And watch this video by Matt. From Shoot to Sale: Part 1 | Adobe Blog

I hope you found this helpful

Best wishes

JG

I see some chromatic aberration, which I believe also falls under the "artifacts" rejection reason.

Your second picture is missing contrast as mentioned, also white balance could be adjusted a bit, and composition could be improved.

But you also have a problem with lens flare, and at times lens flare can be used in a good way - here it doesn't work, so that can also be a reason for the 'Technical Issues' rejection.

Your spiderweb photo also has problems as already mentioned - your highlights are blown out - too bright. (Blown out meaning there is no detail that can be recovered.) Maybe the reviewer also saw the reflected parts of the web as artifacts which can be seen at 100% hence the 'artifacts' reason.

Read this:

Quality and technical issues rejected at Adobe Stock

Let‘s face it ... the first image, who would buy it ..? It’s a mess. The second one could be ok if you worked with it. Terrible lighting - the leaves in the sides are too dark. Light them up and make them green. And remove the ugly reflections in the lower leaves. Flowers and other plants are a very saturated market with lots of competition from great photograpers. But then again - you never know ...

Let‘s do the second one first: The picture is missing contrast. Adobe does not really like such pictures...

The first one is clearly having problems in the highlights that are completly blown out at regions where they shouldn‘t:

As for the size: images should have at least 4 Mpixels. That is a very low requirements as modern cameras have between 16 and 60M pixels.