It's not a bribe. A bribe would be if Qualcomm offered a personal reward to Apple execs for using their chips. This was a price reduction meant to keep a key buyer of chips from choosing competitors. It's a key difference.

For example, Amazon Web Services can offer discounts to keep companies from switching to Azure and Google Cloud. That's legal. If Amazon Web Services offered the CEO of Snap a billion dollars (to them personally, not to the company) to use AWS instead of Google Cloud, that's illegal (both for AWS to offer it and for the CEO to accept it).

The only reason why it's illegal for Qualcomm to have taken this action is because it falls afoul of competition regulations. For example, AWS may be the largest cloud provider and it may be a key market, but they aren't so large that they can really shut off the market to competitors. Similarly, none of their customers are so large that they're a significant portion of the market for buying servers. Finally, because AWS doesn't control buying servers or data centers (and companies often do invest in that when they hit a certain scale), it's hard to argue that they're shutting out competition.

By contrast, Qualcomm specifically created a plan to make sure it wouldn't be profitable for competitors to develop high-end modems. While more Android phones are sold than iPhones, the iPhone is a very significant portion of the high-end phone (and modem) market. If Apple committed to Intel or another manufacturer, that company would have the sales necessary to create high-end modems that would challenge Qualcomm. Absent Apple committing to that, it's unlikely that any company would be willing to spend the money developing competition to Qualcomm. Plus, Qualcomm's discounts mean that a company like Intel would look at the situation and note that if they did develop a competitor, Qualcomm would simply discount their chips for a year or two and drive them out of the business. If you're Intel and you develop a competitor and no one buys your chips for a couple years, you'll exit the business.

You're allowed to offer discounts to get companies to choose your products or stay with your products. However, you're not allowed to use discounts to choke off competition.

From what I understand of the situation Qualcomm is accused of: 1) Qualcomm has patents on LTE and other wireless technology that they committed to licensing under FRAND (fair, reasonable, and non-discriminatory) terms. 2) If you want Qualcomm chips, you need to agree to a license for those patents on Qualcomm's terms and not challenge the terms as violating FRAND. 3) Because Qualcomm got you to agree to very high licensing rates for their patents, they could then discount their chips a lot to keep competitors from getting a foothold.

Let's say you're Apple. You need Qualcomm's modems because they're the only high-end modem supplier in the world. So you agree to their non-fair license rates. Intel looks like they might enter the market and create a second seller of high-end modems. Qualcomm offers a steep discount on chips so that you won't buy Intel's and so Intel doesn't have enough sales to continue in the market. You have to pay Qualcomm's very high non-fair license rates even if you use Intel chips because you still need Qualcomm chips for some of your phones. Qualcomm's discount on their modems came with the caveat that you only use Qualcomm modems. So, Apple could buy some modems from a competitor, but they'd still have to pay Qualcomm's very high license rates and more for the Qualcomm chips they needed -or- they could take the discount on Qualcomm chips.

Over the past two generations of iPhone, Apple has been trying very hard to break Qualcomm's monopoly. They're propping up Intel's modem business with the hopes that they can switch 100% off Qualcomm in the future and get rid of what they see as Qualcomm violating their FRAND licensing requirements. But they couldn't do that without a competitor for modems. Because Qualcomm operated "no license, no chips" and Apple couldn't shut down iPhone production for years until a competing high-end modem came around, they had to play ball. At this point, they only really need Qualcomm for Sprint and maybe some other small carriers. In a pinch, Verizon does have non-CDMA, VoLTE-only (voice over LTE) phones.

It is illegal to accept bribes, but this isn't a bribe. A bribe would have been to offer a reward to some Apple execs to tip the scale in Qualcomm's favor against Apple's interests. "If your town chooses us for your broadband, you might find a new Porsche in you driveway," is a bribe. "If your town chooses us for your broadband, we'll charge residents 20% less than Comcast," isn't a bribe. "...we'll also upgrade the town's electrical system...we'll sponsor after-school coding classes for students in town...we'll throw a dance party for everyone in town," aren't bribes because the benefit isn't a personal one for the person making the decision. Qualcomm isn't accused of offering a bribe to key execs at Apple. If Qualcomm's actions hadn't been anti-competition, there's nothing wrong with discount payments. Almost all companies offer discounts off list prices if they're dealing with enterprises. The issue is that it's anti-competition and that's why Qualcomm is the only one in hot water. Apple wants the competition and has been doing more to stimulate it than anyone else seems to have been.