• You have not described the purpose of payload. If this is a JSON payload going to some other web service, Not found is a poor choice for a missing value and None would be more appropriate
• You never use payload['store']
• Your selector h1[class="product-page-header"] should just be h1.product-page-header
• I think your regex for JetshopData is unnecessarily permissive. If the format breaks, you should be notified by a parse failure rather than silently letting a changed design through - since the outer dictionary format will likely not be the only thing to change
• You should constrain your regex to only looking in <script> values rather than through the entire HTML document
• '{}'.format is redundant
• Tell requests when you're done with the response via context management; conversely, there is no benefit to del bs4 if you have proper method scope
• It's likely that you should be looking at all variations instead of just the first
• Don't blanket-except. If you get a specific exception that you want to ignore that, ignore that in a narrow manner.
• Separate your scraping code from your payload formation code

The following suggested code uses BeautifulSoup because it's what I'm more familiar with and I didn't want to bother installing selectolax:

import json
import re
from dataclasses import dataclass
from pprint import pprint
from typing import Optional, List

import requests
from bs4 import BeautifulSoup


@dataclass
class Product:
    name: Optional[str]
    price: Optional[str]
    image: Optional[str]
    sizes: List[str]

    @staticmethod
    def get_sizes(doc: BeautifulSoup) -> List[str]:
        pat = re.compile(
            r'^<script>var JetshopData='
            r'(\{.*\})'
            r';</script>$',
        )
        for script in doc.find_all('script'):
            match = pat.match(str(script))
            if match is not None:
                break
        else:
            return []

        data = json.loads(match[1])
        return [
            variation
            for get_value in data['ProductInfo']['Attributes']['Variations']
            if get_value.get('IsBuyable')
            for variation in get_value['Variation']
        ]

    @classmethod
    def from_page(cls, url: str) -> Optional['Product']:
        with requests.get(url) as response:
            if not response.ok:
                return None
            doc = BeautifulSoup(response.text, 'html.parser')

        name = doc.select_one('h1.product-page-header')
        price = doc.select_one('span.price')
        image = doc.select_one('meta[property="og:image"]')

        return cls(
            name=name and name.text.strip(),
            price=price and price.text.strip(),
            image=image and image['content'],
            sizes=cls.get_sizes(doc),
        )

    @property
    def payload(self) -> dict:
        return {
            "name": self.name or "Not found",
            "price": self.price or "Not found",
            "image": self.image or "Not found",
            "sizes": self.sizes,
        }


def main():
    product = Product.from_page("https://shelta.se/sneakers/nike-air-zoom-type-whiteblack-cj2033-103")
    if product is None:
        print('No new payload')
    else:
        print('New payload:')
        pprint(product.payload)


if __name__ == '__main__':
    main()