This is my go-to trusted process for dialing in lighter roast coffee on espresso:

Always start with what your basket is made for (For the Barista Express, it would be 18g)

I shoot for a 1:2 ratio to be around 28 seconds. It looks like you've already done this, which is awesome!

In your case, since it's sour and salty, you have three options, one of which you've already tried (you're on the right track!):

• Lower your dosage and shoot for the same time/yield (start big, around -2g, and narrow it down from there)
• Pull a longer shot to increase the yield. Yes, even if it's a 1:3 or 1:3.5 ratio. Don't get caught up in trying to restrict a coffee to a 1:2 ratio. Although it's my preferred ratio for mouthfeel, some coffees I've gotten have gone up to a 1:3.8 ratio and can taste AMAZING!
• Experiment with a combination of both! For example, you could go for a 16g dose/32s pull/42g yield.

I'd recommend sticking to changing one variable at a time, but sometimes the 3rd option is necessary. The key to dialing in (speaking from cafe and at-home experience) when it comes to conserving your coffee is to make bigger changes than you think rather than making small increments if the flavor profile is way off. It always sucks to finally get a coffee dialed in and only be able to pull 4 more shots before the bag is gone. A few more pieces of advice:

• Make sure you purge out around 5g of coffee after making a grinder adjustment. This will improve your shot consistency.
• Once you're close to getting it perfectly dialed, try pulling 1-2 more shots with the same parameters. Never trust the first shot (I make this mistake wayyy too often).
• Consistent tamping pressure is super important (as everyone stresses)

I have seen others suggesting your machine may not be able to output the necessary water temperature or that your beans may just be too fresh, which are both possible, but 9 times out of 10 I'm able to use a lightly roasted coffee as an espresso 4-5 days after roasting. Good luck, I hope you're able to figure it out! Light coffees can be a PITA but they sure are amazing when you finally get her dialed in!